abstreet/docs/design/biking.md

Biking-related design notes

Bike lanes

How do we model bikes merging to a driving lane to make a left?

General modeling

Bikes are just like cars and can use all the same code, right? Except...

• different speeds
• can use bike or driving lanes
• they dont park or unpark
  • actually, how does a ped start/stop using a bike?
  • modeling bike lockup locations is overkill. in practice not a problem. fixed 60s penalty to start/stop biking. penalty happens on the sidewalk, then they spawn onto the bike/driving lane at the very end
• they can maybe overtake on a bike lane?
  • nah, that should be modeled as two bike lanes (or a bike and driving lane) and normal lanechanging behavior
• different rendering
• dont want to use CarID; could maybe rename it VehicleID, but then bike-specific code (like rendering) gets weird

Because of the orchestration with walking/biking models, I'm tempted to try to share some common code, but keep things a bit separate. However, if they're separate...

• driving lookahead needs to see bikes and vice versa
  • do the SimQueues need to be state that both models can access?

Do this in a branch for sure. Roughly:

• introduce BikeID, the rendering, stubs for spawning
• lift SimQueues into Sim
• refactor lookahead
• add biking model

After starting this, I'm not sure now. The driving model as-is can handle bikes fine. The interaction with the walking sim to appear/disappear is pretty minimal. Alternate idea for another branch:

• keep existing driving code almost entirely as is. = Vehicle bike type with super slow speed, modify driving lookahead to use the cap speed. = no BikeID, just a bit in Car for is_bike. = spawn param to decide if a trip without an owned car will instead bike = walking state can own the 'parking/unparking' state. = need a new DrivingGoal, simpler than ParkNear. = render peds doing bike prep differently

  • make sure biking from border works, needs an extra bit i think

  • entirely new render code, but the same DrawCarInput (plus is_bike bit). that part shouldn't matter, right?

  • lastly: rename. Car -> Vehicle? Vehicle -> VehicleParams? DrivingSim -> QueuedSim?

  • etc

    • stats; driving.count and trip score

    • vehicle enum instead of is_bus, is_bike

    • spawn commands getting to have lots of similarish cases

    • reusing DrivingGoal to mean bike start point too?

    • calculate_paths in spawn needs plumbing. introduce a PathfindingRequest struct, avoid those bools.

    • remove the sim helpers that do specific stuff... think of another way to set up tests, similar to tutorial mode?

    • verify abtest consistency

    • all of the get_blah_from_blah queries in map are a mess

    • Position(lane, dist) type would help, yeah?

    • a big help: get rid of dimensioned. make Eq work by wrapping NotNaN or something else, maybe even requiring explicit tolerance thing? get rid of all the terrible PartialEq hacks.